OFFSET
-1,2
COMMENTS
LINKS
G. C. Greubel, Table of n, a(n) for n = -1..1000
Michael Somos, Introduction to Ramanujan theta functions
Eric Weisstein's World of Mathematics, Ramanujan Theta Functions
FORMULA
Expansion of (1/q) * (phi(-q) * psi(q^4)) / (phi(-q^3) * psi(q^12)) in powers of q where phi(), psi() are Ramanujan theta functions.
Expansion of eta(q)^2 * eta(q^6) * eta(q^8)^2 * eta(q^12) / (eta(q^2) * eta(q^3)^2 * eta(q^4) * eta(q^24)^2) in powers of q.
Euler transform of period 24 sequence [ -2, -1, 0, 0, -2, 0, -2, -2, 0, -1, -2, 0, -2, -1, 0, -2, -2, 0, -2, 0, 0, -1, -2, 0, ...].
G.f. is a period 1 Fourier series which satisfies f(-1 / (24 t)) = 3 / f(t) where q = exp(2 Pi i t).
a(n) = A058573(n) unless n = 0.
EXAMPLE
1/q - 2 + 2*q^2 - q^3 - 2*q^4 + 4*q^5 - 2*q^6 - 2*q^7 + 6*q^8 - 4*q^9 + ...
MATHEMATICA
QP = QPochhammer; s = QP[q]^2*QP[q^6]*QP[q^8]^2*(QP[q^12] / (QP[q^2]* QP[q^3]^2*QP[q^4]*QP[q^24]^2)) + O[q]^60; CoefficientList[s, q] (* Jean-François Alcover, Nov 16 2015, adapted from PARI *)
PROG
(PARI) {a(n) = local(A); if( n<-1, 0, n++; A = x * O(x^n); polcoeff( eta(x + A)^2 * eta(x^6 + A) * eta(x^8 + A)^2 * eta(x^12 + A) / (eta(x^2 + A) * eta(x^3 + A)^2 * eta(x^4 + A) * eta(x^24 + A)^2), n))}
CROSSREFS
KEYWORD
sign
AUTHOR
Michael Somos, Feb 05 2012
STATUS
approved